Calutron receivers



N0V- 29, 1955 J. G. BAcKUs 2,725,477

CALUTRON RECEIVERS Filed May 28, 1945 3 Sheets-Sheet l ATTORNEY.

Nov. 29, 1955 J. G. BAcKUs CALUTRON RECEIVERS 3 Sheets-Sheet 2 Filed May 28, 1945 INVENTOR. JOHN 6. BAcKc/s ATTORNEY.

Nov. 29, 1955 Filed May 28, 1945 Fig. s.

J. G. BACKUS CALUTRON RECEIVERS 3 Sheets-Sheet 3 INVENTOR.

doH/v G. BAC/As BY /Kntu// ATTORNEY.

`vergence ofthe paths of travel of the ions of United States Patent Office 2,725,477 Patented Nov. 29, 1955 l CALUTRN RECEIVERS Application May 2s, 194s, serial No. 595,225

. 1o canas. (ci. 25o-41.9)

The general subject of this invention involves the separation, based on difference in mass, of minute particles, suchl as atoms, and especially the separation of isotopes of an element or the separation of a portion of an `element enriched with respect to a particular isotope on a scale yielding commercially useful quantities of the collected material.

The type of means or mechanism to which the invention relates is known as a calutrom and correspondingly the method or process is known as a calutron method or process. l The essential basic elements of a lcalutron include an evacuated chamber mounted in a magnetic field and containingapparatus `for ionizing a polyisotope to be treated, apparatus for projecting a beam of ionized particles of the polyisotope along paths determined by the masses .of the respective ions, and a target apparatus for deionizing theparticles of the beam and for retaining at least one selected v.isotope component in a separated region from which it can be recovered.

in its presently preferred form, the calutron comprises an evacuated tank placed between the poles of an electromagnet so that the evacuated space within the tank tank is pervaded with a magnetic field of high flux density. Within thetank there is provided a source unit thatincludes means for supplying the polyisotope as a vapor or gas to an ionizing region, ionizing apparatus for producing positively ionized particles from the vapor, landan accelerating device maintained at a high negative electrical potential with respect to the ionizing apparatus for withdrawing they positive ions and imparting toeach of them a predetermined energy in the form of substantially uniform velocities along paths generally normal to the direction of the magnetic field toward a beam defining slit in the accelerating device disposed generally parallel to the direction of the'magnetic field.

The accelerated ions move transversely .to themagnetic field and are constrained to travel along arcuate paths having radii that vary with the vmasses of the particle. By virtue of the accelerating slit construction, the paths for the ions of a given mass diverge from a median path to an extent determined by the geometry of the ionizing and accelerating devices. This' dia given mass continues through the first 90 of arcuate travel, andthen the paths converge during the next 90 land cross each other in a region of focus approximately 180 from the source unit. Thus, in effect, geometrical focusing of a ribbon-shaped stream of ions of a given mass ,is accomplished adjacent the 180 point, even though there is a relatively wideangle of divergence of the ions at their source.

Similarly, the ions of any other given mass travel along paths that define a ribbon-shaped stream coming to a focusl at approximately 180 from the accelerating apparatus. Being composed of ions of different masses, the streams olf ions' of different isotopes have .radiih'of curvature that differ by an amount dependent solely upon the mass difference of their respective constituent ions. As a result, the centers of the foci of the streams of different isotopes are spaced apart by an amount approximately equal to the difference in the diameters of their respective median paths. In the case of the heavier elements, such as uranium, the difference in mass between the isotopes is not suiiicient for accomplishing complete separation of the streams in which the ions of the different isotopes respectively travel,y while employing a practical minimum divergence of the beam at the beam defining slit, and a plurality of overlapping streams having overlapping regions of focus are created.

A receiver is disposed within the vacuum tank adjacentthe foci of the isotope ions to be separated, for deionizing them and for separately collecting.,one or all of them as may be desired. Because of thek neces` sary overlapping of the streams at their foci, it is impractical in one operation to separate completely the isotopes of the heavier elements, and, in practice, the separated quantities of material collected at the receiver are merely enriched with respect to a particular isotope.

The degree of isotopic enrichment that may be achieved in practice is also limited by a phenomenon known as scattering Probably as a result of collisions between ions, or between ions and neutral gas particles, ya certain number of ions of one mass that shouldreach the receiver entirely outside the region o f focus of the ions of a lesser mass, lose lenergy during their travel. After losing energy these ions of greater mass are caused to continue along arcuate pathsof increased curvature, and some of them arrive at Athe receiver within the portion of the beam richest in` a lighter component, thus increasing the contamination of the lighter component by the heavier component. t In the case of the heavier elements, theclose proximity of the centers of the 180 foci of different isotope components of the beam presents still another complication aiecting the isotopic enrichment obtainable in prac.- tice. The particles reaching the receiver are traveling at high speeds and tend to rebound from the surfaces they first strike, a phenomenon referred to as sputtering. Because the particles do not necessarily rebound from a surface at an angle therewith equal to the angle of collision, sputtered material is showered in many directions from those surfaces of the receiversubjected to direct ion bombardment. As a result, the problem of retaining separated material in a region of a receiver where it first strikesand of preventing contamination of separated material with sputtered particles from another region of the receiver, present serious dificulties. Failure adequately to handle these difficulties may result in a substantial decrease in the separation and retention etliciencies of a receiver. i

For a complete disclosure of a calutron and its mode of operation, reference is made to the copendng application of Ernest O. Lawrence, Serial No. 557,784, filed October 9, 1944, for Methods of and Apparatus for Separating Materials, now Patent No. 2,709,222.

The present invention relates to that part of a calutron referred to as the receiven and only such parts of a calutron will be described herein as are necessary to an understanding of the present invention.

It is an object of the invention to provide an ion receiver which will retain effectively a high percentage of the ions transmitted thereto.

Another object ofthe invention is to provide anion receiveriwhich` will retain ions effectively irrespective of sputtering caused when the ions strike a surface of the receiver pocket.

A further object of the invention is to provide an ion receiver which provides pocket surfaces free from direct ion bombardment and advantageously disposed to permit deposit of deionized particles.

Another object of the invention is to provide an ion receiver which will collect the respective enriched 'com'- ponents of a polyisotope beam in separate compartments or pockets.

Another object of the invention is to provide an ion receiver having a series of trapping walls or blades providing a corresponding series of separate compartments, each wall having one surface exposed to direct ion bombardrnent and the opposite wall protected from direct ion bombardment.

A *further object of the invention is to provide a'n ion receiver having a series of ion trapping walls which are disposed at an angle to the generalvpath of the ion beam so that one surface of each wall is protected frorn direct ion bombardment.

Another object of the invention is to provide an ion receiver having an ion collecting pocket and a current reading electrode adjacent thereto that is employed to monitor the beam and enable proper adjustment thereof for reception of ions by the pocket.

A further object of the invention is to provide a monitoring system for the ion beam in which a delimited portion of the beam is admitted to a current reading electrode so that the beam can be maintained in the desired adjustment by maintaining a constant current reading at the electrode.

l Other objects and advantages will be apparent from the following description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

In Ithe drawings,

A Fignre l is Va horizontal sectional View through a cal" utron ltank illustrating somewhat schematically the arrangement of the source and receiver units within the tank as 'well as the relation of the tank to the magnet ssoeiated therewith; v

i Fig'. 2 is an elevational view, partially in section, of 'the receiver unit taken as indicated by the line 2--2 in Fist 1;

Fig. `3 is a longitudinal sectional view of the receiver finittaken in a plane indicated by the line 3*'-3 in Fig. l;

Fig. 4 is a transverse sectional'view of the receiver tkena's indicated by the line l-4 in Fig. 3;

Fig. 5 is a fragmentary 4view of a portion 'of the receiver unit taken as indicated by the line 5-5 in Fig. 4.

Referring to the drawingsLl-igi illustrates a calu# tren f irradiancia discised in the Lawrence applicatn, 'Serial No. 557,784, previously referred to, and which will described generally in s'o far as the parts corre'- spond to those of the above Lawrence application. The caltion includes a tank which is mounted by a pluralit'y of wheeled supports v11 on a pair of 'track rails 12 on one Ipole face Y13 of the calutron magnet. The

is connected by a conduit 14 to interior of the tank 10 'means for reducing the pressure within the tank, includ"- inga ssuitably constructed 4diffusion pump 1:6 of 'relafiii'y iavrgepcp-eity and a baekin'g mechanical va'uum 17. By operation of the mechanical vand diffusion Xpuurnps,the, pressure within the tank 10 is reduced to a value within the desired range, which is generally of the o rder of from l0?34 Hg to 10-5 mm. Hg.

K 'Within the tank 10, a s'ourceunit 18 is provided for producinga beam of singlypionized positive ions to be transmitted to a receiver unit 19, the beam being indicated by the dot-dash line 21 which is disposed at the 1o- 'cation of a median ion path within the beam. The source unit 18 includes a source block 22 carried by a stem 23 which is lsuitably supported by an insulator- 23a on the side 1vvall of the tank 10. The source block 22 is provided with a cavity l24 to recente a charge of the polyisotope lto be treated, for example, a charge of uranium tetrachloride. The charge within the cavity V24 fis heated in any suitable -i'anne'r to be changed 'to a gas and passes into an arc chamber 25 within the block 22 where it is subjected. to an electric arc to cause ionization of the particles.

The source unit 18 also includes a pair of accelerator electrodes 26 which are disposed in spaced relation from the source block and maintained at a high negative potential with respect thereto towithdraw ions from the arc chamber 25 and accelerate the ions to form the trans mitted ion beam. The accelerator electrodes 26 are supported in a convenient manner by support structure 27 within the tank 10, one of the electrodes 26 having a pivotal support 28 so that the spacing between the electrodes may be varied by means of an adjusting linkage 29 which extends through the side wall of the tank for exterior control. The above described source unit is fully disclosed in the Lawrence application, Serial No. 557,784, to which reference is made for details not shown herein.

It will be understood that the ion beam is composed of ions leaving a region of focus located between the accelerator `electrodes 26 and the arc chamber 25 so that the paths of the ions as they leave the source region are dis= tributed through a given angular divergence to either side of the median path 21 illustrated. It will be under'- stood, of course, that there is a median path `21 for each isotopic component of the total ion beam. As previously explained, from geometrical considerations, the ion paths again converge in a region substantially from the source unit to a region of focus wherein the paths of the ions again possess 4the 'same relative angularity with re`- spect to the median path. A receiver unit 19 is located at the region of focus to receive the ions, to effect deionization, and to collect the deionized particles.

Referring to Figs. 1 and 2, the receiver unit 19 includes a cylindrical shell or casing position generally parallel to the direction of the magnetic field by a tube 32 which extends from one end of the casing 31 and is formed in a reverse curve to provide a tube portion coinciding with an axis of symmetry of the cylinder 31 midway between the ends thereof. The tube 32 *passes through an aperture in the wall 33 and a similar aperture in a closure plate 34 secured to the tank wall. The tube `32 is supported both slidably and ro*- tatably in a combined mounting and seal structure including a plate 36, a seal 37, and a metal bellows 38. This mounting for the collector unit is of the character disclosed in said Lawrence application, Serial No. 557,784.

The receiver unit 19, as previously described, includes the cylindrical casing 31 (Figs. 3-5) which is provided near one end with an opening 40 on one side to admit ions to the interior of the casing and a smaller opening 41 at the opposite side. A third opening in the form of an elongated slot 42 (Fig. 2) is provided below the opening 40 and aligned with one side of the opening 40 for a purpose later described. A pocket structure including a series of similar pockets 43 is disposed withinthe 'casing 31 to face the opening 40 while a current reading electrode 44 is disposed therein to face the opening 41. Thepockets 43 are formed of U'shaped pocket members 46 yofa 'material resistant to ion bombardment and affording easy 'chemical cleansing, for example, platinum foil may be employed. At their ends, the U-shaped pocket members 46 have spacers 47 interposed between the opposed walls thereof, and the spacers 47 and pocket members 46` together with retaining plates 48 and 49 are apertured to receive securing screws S1 which have threaded engagement with the plate 49. l,

The plate 49 (Fig. 3) of the pocket structure is extended at -one end to provide a bent portion 52 secured to 'a washer 53 by a screw 54. The Washer 53 is rotatably seated in a cup-shaped fitting or'retai'ner 56 of suitable insulating material which is held against endwisc movenient out of the casingll by one or more screws v5,7. The plate 49 (Figs. 3 andai) vis also secured-by a pair of screws 58 to an insulator block `459 4whichis"interposed between the potrei stmsfufe 'and are bent ein si @fthe 'cuff-em raaingeleetmae 421. -A u-shaped metallic supporting 31 which is supported in ond bentend 63 secured by'a screw 6-5"to analigning disk 66 similar to the disk 532ml' seated'in asimilar cupshaped retainer 67. The retainer 67 `is seated against al centrally recessed end plug 68,' which is'secured within the casing 31 by a series of screws 69 and houses a flanged insulating plug 7i), The plug 68 (Fig. 3) is provided with a radial recess 71 which is enlarged at its outer end to receive the supporting tubev 32.

In addition to its supporting function, the tube 32 provides a conduit for a pair of electrical leads 72 and 73 enclosed in suitable glass insulators74. The lead 72 extends through a suitable passage in the insulating plug 70 to the screw 65 to provide the electrical lead from the electrodes 44 and 62. The lead 73 also extends through a suitable passage in the insulating plug 76, andl then through an insulating iitting 76 in the aligning disk 66 and thence to one of the securing screws S1 of the pocket structure. The leads 72 and 73 extend to suitable meters 77 and 78 (Fig. 1).

By virtue of the offset or reverse curve construction of the supporting tube 32, the receiver unit can be rotated through 180 to present either the opening 49 or the opening 41 for admission of ions into the receiver structure. During focusing of the beam to obtain steady operation, the opening 41 will be presented so that the ions are admitted therethrough to the electrode 44. The v width of the opening 41 is selected with respect to the total width of the beam in its plane of sharpest focus, and the opening 41 is located so as to admit the beam portion of greatest density. ln the present instance, the opening 41 has a width equivalent to 3 mass units and is located to receive the maximum number of ions for such width. In this way, the current flow resulting from deionization of the particles irnpinging on the electrode 44 can be maximized by appropriate adjustment of the magnetic lield strength and the accelerating voltage to obtain proper beam focus for reception.

When this condition obtains, the receiver unit can be rotated through 180 to present the opening 40 to the ions so that the pockets 43 will receive and retain the material as deionized particles. The width of the opening in the present instance is selected to be equal to or exceed the total width of the beam in its region of sharpest focus. Considering the beam with respect to the isotopes 234, 235, and 238 of uranium, a width corresponding to 6 mass units would be appropriate. It will be understood, of course, that the open ing 40 as shown in Fig. 2 `does not extend for the full depth of the beam in the direction of the magnetic field, and that a portion of the beam also impinges upon the casing 31 wherein the slot 42 is formed, so that ions are simultaneously admitted through the openings 40 and 42. This enables reading of current to the electrode 62 during reception of ions by the pocket structure 43, the opening 42 being so related to the opening 40 that it receives the U238 ions, i. e., the densest portion of the beam. Thus, after appropriate focusing of the beam by use of the opening 41 and the electrode 44, proper beam focus can be maintained during reception by maintaining a maximum current on the electrode 62.

By virtue of the rotative mounting of the respective aligning disks 53 and 66 in their associated collars 56 and 57, the pocket structure, including the pockets 43, canv be rotatably adjusted upon assembly within the casing 31 so that the series of walls formed by the adjacent pocket members 46 will present the desired angle to the oncoming ions. greater than the maximum angular divergence of ions from the median or center ion path as permitted by the This angle should be equal to or conditions obtaining at the source, including thespacing of the accelerating electrodes from thesource block, the, width of the slotin `the source block lfrom which ionsv are withdrawn, andthe spacing apart ofthe accelerator electrodes from each other. v Y l' As shown in the drawings, for example,1Fig`.'4,`an angle of approximately 10 is formed between the walls of the pockets 43 and the median ion path *21. Thus, with this angular relation of the walls of the pockets 43, the' receiver is adjusted for an angular divergence of the ion beam from the source'of :1 -10 or less. In

this fashion, the wall surface 81 of each wall'is subjected to gdirect ion bombardment while the opposite wall surf face 82 is free from such direct", ion bombardment |so that material which impinges upon the wall surface 81 and is reflected or sputtered therefrom can deposit upon the wall surface 82 in each pocket.

Because the number of pockets provided covers the entire spectrum of isotope components present in the beam, the material collected in the respective pockets 43 will reflect the enrichment of the respective components in the different portions of the beam.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modiiications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. In a calutron having a source unit for transmitting an ion beam with ions traversing paths divergent to either side of a median ion path and means for causing convergence of said ion beam in a region of focus, an ion receiver disposed in a region of focus of said ion beam and having a series of similarly disposed ion trapping walls in the path of the beam, with each wall in an acute angular relation to the median path of the ion beam at least as great as the amount of said divergence.

2. In a calutron having a source unit for transmitting an ion beam to a target region, an ion receiver disposed in said target region and having a series of ion trapping walls disposed at an acute angle to the path of the beam to expose one surface only of each wall to direct ion bombardment.

3. In a receiver for a calutron ion beam, an ion collector comprising a series of substantially parallel ion trapping walls disposed at an acute angle to the path of the beam to expose one surface only of each wall to direct ion bombardment.

4. In a receiver for a calutron ion beam, an ion collector comprising a collecting pocket structure having a plurality of adjacent ion trapping walls in said pocket structure, each of said walls being disposed at an acute angle with respect to the beam to expose one surface thereof to direct ion bombardment and to protect the other surface thereof from such direct ion bombardment and thereby provide for retention of sputtered material on said protected surfaces.

5. In a receiver for a calutron ion beam, an ion trapping pocket having a surface exposed to the lion beam and another surface opposed to said lirst surface and protected from the ion beam to receive sputtered material from said first surface. v

6. In a receiver for a calutron ion beam, a collecting unit comprising a pair of adjacent walls disposed in the path of the beam having opposed facing surfaces, one wall surface being exposed to direct ion bombardment and the opposed wall surfacey being protected from ion bombardment to receive sputtered material from said first wall surface.

7. In a receiver for a calutron ion beam composed of ions whose paths in the region of reception vary through a given angular divergence from a median ion path, a

collecting member disposed in the path of said ion beam in said region of reception and at an acute angle to said man?? 8. receiver .for a cal'utijn ion be c'ihp'isig housing having an ope'nr''g disposed to adr'nit4 selected portion of said ion beam and serie'sof si'rhila'r pockets mounted Within Vsaid hos'i'ng -to collect ions passing through Said opening. l

9. In a calutron hai/ing means for establishing an in beam with ions traversing paths divergent lto either side' of a lrnedn ion `path and means for causing 'convergence ofrsad ion beam i a region of focus, anion Areceiver corprsing a collecting pocket and an electrode having a S- face ydisposed adjacent the egion f focus for intereiing' another portion of "che i'on bea.

1t). in ea'liitf 'having mean-sier establishing an ien beiii with ions tiver's'ing paths divergent to `i'dier side f fiidiaii iii path and means for eausing convergen@ of said ion bean; in a 'region of focus, an icm feeiver ecmpiisig cdlie'tiiig pocket for feeeiviiig apcition of th ion beam and aii eleeirde liaviiig a surfaeefo'r interceptiiig oth portieri of said ion beam, said electrode being disposed to ieeeive a siiiiii'f' biit more delimited portion than ihi'received by said packet.

References Cite in the le of this patent UNITE rSTATES PATENTS 

1. IN A CALUTRON HAVING A SOURCE UNIT FOR TRANSMITTING AN ION BEAM WITH IONS TRAVERSING PATHS DIVERGENT TO EITHER SIDE OF A MEDIAN ION PATH AND MEANS FOR CAUSING CONVERGENCE OF SAID ION BEAM IN A REGION OF FOCUS, AN ION RECEIVER DISPOSED IN A REGION OF FOCUS OF SAID ION BEAM AND HAVING A SERIES OF SIMILARLY DISPOSED ION TRAPPING WALLS IN THE PATH OF THE BEAM, WITH EACH WALL IN AN ACUTE ANGULAR RELATION TO THE MEDIAN PATH OF THE ION BEAM AT LEAST AS GREAT AS THE AMOUNT OF SAID DIVERGENCE. 